How to Perform a Network Inventory

Network managers can't effectively manage the network if they're not aware of all the devices it includes.

Inventory management tools can discover existing hardware and software and document version, location and IP address information. Such knowledge aids configuration management, support and maintenance. To use these tools most efficiently and make the best use of the collected data, heed these pointers.

1. Be Broad

Finding every device on a network takes several techniques all working together. Traditional IP-based network scanning works for well-configured devices that want to be found. However, network managers should also look for misconfigured devices or those that are hiding or not answering. A successful inventory tool combines multiple techniques, starting with easy tasks (such as IPv4 and IPv6 scanning) and moving on to more difficult ones (such as inspecting MAC forwarding tables and Address Resolution Protocol tables in switches, routers and firewalls).

Passive inventorying and fingerprinting (using mirror ports on switches or network taps to watch network traffic and see what systems are actually talking) also offers significant advantages because as soon as a system becomes active, it can be detected. Several intrusion prevention systems feature passive fingerprinting, and this can be a great source of data for a network inventory project. Active scanning, on the other hand, has the potential to disrupt older systems and needs to wait for the scanner to get to a particular network segment. Mixing multiple techniques provides the most current and accurate results.

2. Be Open

Network inventory information can aid many aspects of IT management, from the security team to the help desk to patch management and more. But there's a danger in trying to make one tool do all these things, because each constituency within IT, networking and security will have different needs and requirements. No single product can cover all bases. The solution is to use products that have open interfaces, such as documented database structures.

A successful inventory system lets data flow smoothly between different functions — such as IP address management, help desk inventory, security and vulnerability analysis and desktop management — rather than hoping to find all functions in a single tool. IT managers may need to integrate different tools or export data from one to another, but the benefits of linking open tools make this a worthwhile task.

3. Be Strategic

The term "inventory" has a lot of meanings, so it's helpful to focus narrowly on a goal.

Without a sharp set of requirements that solve an immediate problem, these projects can get out of hand quickly. IT groups that have adopted the IT Infrastructure Library (ITIL, a hot trend in the world of IT service desks) are especially vulnerable because ITIL adoption requires a lot of software such as device configuration and inventory management.

By setting a clear strategy, IT groups can avoid scope creep and focus on an achievable result with a distinct point of view. From there, using open interfaces to either build on an existing database or export to other tools becomes an easy way to add functionality once things are up and running.

4. Be Skeptical

Any good network inventory tool will uncover an immense amount of useful information very quickly. It's tempting to be starstruck at all the new information and forget that every tool has limitations. Savvy IT managers will remember that there will always be something missing or incorrect, and they will plan for manual updates and domain-specific information to help draw a more complete picture.